Low-friction sliding mechanism including lubricant composition

ABSTRACT

The present invention provides a low-friction sliding mechanism comprising a lubricant composition on a sliding plane between a DLC-coated sliding member (A) and a sliding member (B), wherein the DLC-coated sliding member (A) is formed by coating a base material with diamond-like-carbon containing 10 atom % or less of hydrogen, the sliding member (B) includes at least one kind of material selected from the group consisting of a metal material, a non-metal material, and a metal or non-metal coated material having a surface coated with a thin film, and the lubricant composition contains a basic oil (C), PAG (D), and an acid oxygen-containing organic compound (E) with an acid number of more than 1 mgKOH/g.

FIELD OF THE INVENTION

The present invention relates to a low-friction sliding mechanism including a lubricant composition containing polyalkylene glycol and an acid oxygen-containing organic compound.

BACKGROUND OF THE INVENTION

Lubricants used for machines are required to have higher wear resistance and fuel-saving property. More and more machines, particularly the machines used for an automobile component, which are required to have the fuel-saving property, have come to employ a DLC film for the sliding component. As an additive that provides the effect of reducing the friction, an oily agent such as ester, a fatty acid, and amine have been used, as reported in JP-A-2005-68171.

According to some reports (“Friction induced phase transformation of pulsed laser deposited diamond-like carbon” A. A. Voevodin, et. al., Diamond and Related Materials 5(1996) 1264-1269; and “Effect of Thermal Annealing on Tribological and Corrosion Properties of DLC Coatings” Linlin Wang, X. Nie, and Xin Hu, Journal of Materials Engineering and Performance Volume 22(10) October 2013 3093-3100), friction causes the DLC surface to be carbonized (increase in sp2) and therefore softened. In view of this, the higher fuel-saving property that leads to the higher effect of reducing the friction in the presence of the DLC film has been desired. If the coefficient of friction is low, the friction heat generation is reduced, thereby suppressing the reported carbonization (increase in sp2) due to the friction on the DLC surface and the resulting softening of the surface. This may enable the DLC to have higher wear resistance. Furthermore, the lower friction resistance leads to the smaller stress in the DLC or between the DLC portion and a member below the DLC portion, thereby suppressing the problem of the separation of the DLC film. This enables the DLC lubricant system to continue for a long time.

SUMMARY OF THE INVENTION

The present invention has been made in view of such circumstances, and an object thereof is to maintain the DLC lubricant system for a long time by further reducing the friction.

As a result of concerted studies for achieving the above object, the present inventors have discovered that an adsorbate derived from an ash-free friction modifier formed between the DLC film and the metal is changed into the material more effective in reducing the friction by adding a higher alcohol mainly containing polyalkylene glycol (PAG), and this provides the synergistic effect of PAG and the ash-free friction modifier, particularly an acid oxygen-containing organic compound.

DETAILED DESCRIPTION OF THE INVENTION

An aspect of the present invention is a low-friction sliding mechanism including a lubricant composition on a sliding plane between a DLC-coated sliding member (A) and a sliding member (B). The DLC-coated sliding member (A) is formed by coating a base material with diamond-like-carbon (DLC) containing 10 atom % or less of hydrogen. The sliding member (B) includes at least one kind of material selected from the group consisting of a metal material, a non-metal material, and a metal or non-metal coated material having a surface coated with a thin film. The lubricant composition contains a basic oil (C), PAG (D), and an acid oxygen-containing organic compound (E) with an acid number of more than 1 mgKOH/g.

Preferably, the diamond-like-carbon contain 0.5 atom % or less of hydrogen.

A further embodiment of the present invention is a low-friction sliding mechanism including a lubricant composition on a sliding plane between a DLC-coated sliding member (A) and a sliding member (B). In this embodiment, the DLC-coated sliding member (A) is formed by coating a base material with a-C diamond-like-carbon without hydrogen. The sliding member (B) includes at least one kind of material selected from the group consisting of a metal material, a non-metal material, and a metal or non-metal coated material having a surface coated with a thin film. The lubricant composition contains a basic oil (C), PAG (D), and an acid oxygen-containing organic compound (E) with an acid number of more than 1 mgKOH/g.

Preferably in the low-friction sliding mechanism of the present invention, the metal material of the sliding member (B) is at least one kind of material selected from the group consisting of a material containing iron, a material containing aluminum alloy, and a material containing magnesium alloy. The coated material is formed by being coated with the thin film of at least one kind of material selected from the group consisting of DLC and ceramics.

Also preferably, the PAG (D) is at least one kind selected from the group consisting of polyethylene glycol, polypropylene glycol, and polybutylene glycol. The PAG (D) has a weight-average molecular weight of from 200 to 10,000.

In an embodiment of the present invention, the PAG (D) is present in an amount in the range of from 0.1 to 20.0% based on the entire amount of the lubricant composition.

Preferably, the acid oxygen-containing organic compound (E) has a carbon number of 8 to 1,000.

Also preferably, the acid number of the acid oxygen-containing organic compound (E) is 1.2 mgKOH/g or more.

Preferably, in the low-friction sliding mechanism of the present invention, the lubricant composition contains the acid oxygen-containing organic compound (E) in an amount in the range of from 0.05 to 5.0% based on the entire lubricant composition. It is also preferred that the acid oxygen-containing organic compound (E) contains at least one kind selected from the group consisting of alcohols, esters, ethers, ketones, aldehydes, carbonates, and derivatives thereof.

The present invention also provides a lubricant system including the low-friction sliding mechanism as described herein.

According to any of the aspects of the present invention, the function of reducing the friction of DLC can be further increased by adding an acid oxygen-containing organic compound to a system with PAG added to a basic oil. 

1. A low-friction sliding mechanism comprising a lubricant composition on a sliding plane between a DLC-coated sliding member (A) and a sliding member (B), wherein: the DLC-coated sliding member (A) is formed by coating a base material with diamond-like-carbon containing 10 atom % or less of hydrogen; the sliding member (B) includes at least one kind of material selected from the group consisting of a metal material, a non-metal material, and a metal or non-metal coated material having a surface coated with a thin film; and the lubricant composition contains a basic oil (C), PAG (D), and an acid oxygen-containing organic compound (E) with an acid number of more than 1 mgKOH/g.
 2. The low-friction sliding mechanism according to claim 1, wherein the diamond-like-carbon contains 0.5 atom % or less of hydrogen.
 3. A low-friction sliding mechanism comprising a lubricant composition on a sliding plane between a DLC-coated sliding member (A) and a sliding member (B), wherein: the DLC-coated sliding member (A) is formed by coating a base material with a-C diamond-like-carbon without hydrogen; the sliding member (B) includes at least one kind of material selected from the group consisting of a metal material, a non-metal material, and a metal or non-metal coated material having a surface coated with a thin film; and the lubricant composition contains a basic oil (C), PAG (D), and an acid oxygen-containing organic compound (E) with an acid number of more than 1 mgKOH/g.
 4. The low-friction sliding mechanism according to claim 1, wherein: the metal material of the sliding member (B) is at least one kind of material selected from the group consisting of a material containing iron, a material containing aluminum alloy, and a material containing magnesium alloy; and the coated material is formed by being coated with the thin film of at least one kind of material selected from the group consisting of DLC and ceramics.
 5. The low-friction sliding mechanism according to claim 1, wherein: the PAG (D) is at least one kind selected from the group consisting of polyethylene glycol, polypropylene glycol, and polybutylene glycol, and the PAG (D) has a weight-average molecular weight of from 200 to 10,000.
 6. The low-friction sliding mechanism according to claim 1, wherein the PAG (D) is present in an amount in the range of from 0.1 to 20.0% based on the entire amount of the lubricant composition.
 7. The low-friction sliding mechanism according to claim 1, wherein the acid oxygen-containing organic compound (E) has a carbon number of from 8 to 1,000.
 8. The low-friction sliding mechanism according to claim 1, wherein the acid number of the acid oxygen-containing organic compound (E) is 1.2 mgKOH/g or more.
 9. The low-friction sliding mechanism according to claim 1, wherein the lubricant composition contains the acid oxygen-containing organic compound (E) in an amount in the range of from 0.05 to 5.0% based on the entire amount of the lubricant composition, and the acid oxygen-containing organic compound (E) contains at least one kind selected from the group consisting of alcohols, esters, ethers, ketones, aldehydes, carbonates, and derivatives thereof.
 10. A lubricant system comprising the low-friction sliding mechanism according to claim
 1. 